The emulsion polymerization of a water-insoluble ethylenically unsaturated monomer long has been utilized to form solid polymeric particles that are intended for a variety of end uses. During the polymerization small droplets of liquid monomer are provided at an elevated temperature while suspended in a continuous aqueous phase. In the prior art it has been a common practice to include a water-soluble surface active agent within the aqueous phase that aids in the desired maintenance of the suspended monomer as small spheres wherein the polymerization commonly takes place via a free-radical mechanism. Commonly the water-soluble surface agents are anionic, nonionic, or mixtures of anionic and nonionic surfactants.
When the resulting polymeric particles are utilized in coating and/or adhesive applications, residual surface active agent remaining from the polymerization reaction can be detrimental and can interfere with the performance of the resulting latex and products derived from the final latex. For instance, if dissolved ionic compounds are encountered, this can lead to a destabilization of the suspended polymeric particles and cause an unwanted coagulation of the polymeric particles. Also, when applied to a substrate to form a coating and/or adhesive, the residual surfactant can interfere with the desired adhesion to the substrate particularly if the surfactant concentration is more than a small amount. The scrubability and water sensitivity of a resulting film can be adversely influenced. Additionally, residual surfactant can sometimes cause an undesirable "blooming" that leads to surface irregularities in a resulting polymeric film or layer once it is applied to a substrate.
Heretofore, in some instances it has been proposed to employ certain polymerizable surfactants during an emulsion polymerization process. See, for instance, U.S. Pat. Nos. 4,049,608 and 5,162,475. Additionally, an epoxy resin can be provided to react with residual surfactant as disclosed in U.S. Pat. No. 3,941,857. Polymerizable substances such as allyl alcohol have been found to lead to the formation of undesirably large concentrations of coagulum in the resulting product.
It is an object of the present invention to provide an improved emulsion polymerization process for forming discrete polymeric particles that are well suited for use in coating and/or adhesive applications.
It is an object of the present invention to provide an improved emulsion polymerization process for forming discrete polymeric particles wherein the surfactant utilized during the polymerization does not interfere with the quality of a layer of a coating and/or adhesive formed by the resulting polymer.
It is an object of the present invention to provide an improved emulsion polymerization process wherein the resulting suspension of dispersed polymeric particles is not rendered unstable by the presence of dissolved ionic compounds.
It is an object of the present invention to provide an improved emulsion polymerization process wherein the resulting suspension of dispersed polymeric particles exhibits an enhanced mechanical stability and the ability to withstand freezing and thawing while retaining good particle dispersion.
It is an object of the present invention to provide an improved emulsion polymerization process wherein the resulting polymeric particles exhibit improved adhesion to a substrate when applied as a coating and/or an adhesive.
It is another object of the present invention to provide an improved emulsion polymerization process wherein coatings formed from the resulting product tend to remain uniform and stable upon the passage of time even when exposed to water at an elevated temperature.
It is a further object of the present invention to provide discrete solid polymeric particles that are well suited for use in coating and/or adhesive applications.
These and other objects and advantages, as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.